Advances in digital processing are significantly impacting many endeavors in science and technology and digital processing applications. There are many situations which require converting fast analog signals into digital representation for processing and to harness the power of digital equipment. A key element is a device know as an analog-to-digital converter (A/D converter) which is a crucial front-end in many systems. However, the performance of A/D converters is lagging behind digital processors, creating an obstacle to full digitization of numerous applications.
It would be desirable to provide A/D converters operating between 30 MHz and 3 GHz with resolution in excess of about 10 bits. These A/D converters could be used as components in radar front-ends, intercept receivers, image processing, HDTV and in many other areas. Conventional semiconducting devices have well-known system limitations and cannot meet the above performance requirements. For instance, present silicon bipolar technology achieves 4 bits at 1 GHz and GaAs heterojunction bipolar transistor (HBT) technology is projected to achieve 6 bits at 1 GHz. This leaves Josephson junction (JJ) technology as the most promising to potentially produce the performance necessary for advanced digital systems. The fastest Josephson junction flash A/D converter operated at liquid He temperature achieved 6 bits at 1 GHz, and 3 bits at 10 GHz. These low critical temperature (Tc) circuits require good quality Josephson junctions which have high non-linearity which cannot be reproduced using high Tc (HTC) superconductivity. Consequently, many known low Tc JJ circuits and concepts may not be implemented in HTC superconductivity. It is, therefore, safe to conclude that such known technologies reach their fundamental limitations at performance levels well below what is needed, and a search for new approaches is both warranted and timely.
Therefore, there remains a need in the art for a new A/D conversion system and method based on HTC superconductivity that produce performance levels orders of magnitude higher than what was thought possible using conventional low Tc JJ devices. In particular, a need exists for an A/D conversion system capable of bandwidths in excess of 10 GHz at 10-bit resolution, which is impossible to achieve by previously-known technologies.